The present invention relates to a multi-piece solid golf ball. More particularly, it relates to a multi-piece solid golf ball having excellent flight performance when hitting at low head speed or by an iron club, by accomplishing high rebound characteristics and high launch angle, and having good shot feel at the time of hitting.
In the history of golf balls, a thread wound golf ball has been firstly developed. The thread wound golf ball is obtained by winding thread rubber in a stretched state on a solid or liquid center to form a thread wound core and covering it with a cover of balata, etc. having a thickness of 1 to 2 mm.
A two-piece solid golf ball has been subsequently developed, which is composed of a core formed from integrally molded rubber material and a thermoplastic resin cover (e.g. ionomer resin cover) formed on the core. The two-piece solid golf ball is easily produced because of simple structure, and has excellent rebound characteristics and excellent durability. Therefore, the two-piece solid golf ball is generally approved or employed by many golfers, mainly amateur golfers.
However, the two-piece solid golf ball exhibits harder and poorer shot feel at the time of hitting than the thread wound golf ball.
In order to provide a two-piece solid golf ball having a shot feel as good as the thread wound golf ball, a soft type two-piece solid golf ball using a softer core has been proposed. However, the use of the soft core adversely affects on rebound characteristics, thus resulting in a reduction in flight distance and a deterioration in durability.
It has been proposed to place an intermediate layer between the core and the cover of the two-piece solid golf ball to form a three-piece solid golf ball so as to maintain the balance between flight performance and shot feel at the time of hitting. The three-piece solid golf ball generally occupies the greater part of the golf ball market.
For example, a three-piece solid golf ball comprising a two-piece core composed of a core and an intermediate layer, which is formed from vulcanized rubber material having the same composition as the core, is suggested in Japanese Patent Kokai publication No. 332247/1996 and the like. However, in these golf balls, the thickness of the intermediate layer is too thin, and it is difficult to obtain sufficient rebound characteristics and high launch angle when hitting at low head speed (particularly, when hitting by a middle iron club and a short iron club).
Three-piece solid golf balls comprising an intermediate layer having thin thickness are also suggested in, for example, Japanese Patent Kokai publication Nos. 313643/1997, 239068/1997 and the like. However, in these golf balls, there have been problems that the rebound characteristics are degraded and the shot feel is hard and poor, because the intermediate layer is formed from thermoplastic resin.
A main object of the present invention is to provide a multi-piece solid golf ball having excellent flight performance when hitting at low head speed, by accomplishing high rebound characteristics and high launch angle, while maintaining good shot feel at the time of hitting.
According to the present invention, the object described above has been accomplished by adjusting the diameter, center hardness and hardness distribution of the inner core, the thickness and surface hardness of the outer core, the hardness distribution of the core, and the thickness and hardness of the cover to a specified range. The present invention can provide a multi-piece solid golf ball having excellent flight performance when hitting at low head speed, by accomplishing high rebound characteristics and high launch angle, while maintaining good shot feel at the time of hitting.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.